Safety syringe

ABSTRACT

The present invention discloses a safety syringe and aims to provide simple structure, convenient use, and low cost, and to make the syringe have needle protection functionality and become auto-disable. The present invention includes a sliding casing, a needle, a syringe barrel, a piston, a latching casing, a spring and a plunger inside the syringe barrel, the present invention can be easily used to carry out an injection and to initiate its safety mechanism by a single hand. The sliding casing can be automatically positioned and locked in two directions; This design guarantees during processing the syringe after it is used, the pinhead is always protected by the sliding casing; The present invention also has a reliable function of auto-locking; Therefore, once the syringe is used, the plunger has been locked in the syringe barrel and can not be pulled out any longer; Any attempt to use the syringe again will cause the plunger broken and the syringe damaged, thus ensuring a one-time use.

BACKGROUND OF THE INVENTION

1. Technical field

The present invention relates to a safety syringe, particularly to anauto-disable safety syringe of needle-protective functionality.

2. Background of the Art

At present, more and more diseases are contaminated through blood,bodily fluid, etc. One of main channels that cause disease to spread isusing the same syringe for multiple times and inappropriately handlingthe needle of a syringe after it is used. However, commonly useddisposable syringes may occasionally prick medical staffs afterinjection or hurt the workers processing medical waste later, therebyexisting considerable latent safety problems.

Although there have been many domestic or international patents inrelation to disposable safety syringes, most of the syringes may not bewidely adopted due to complicated configuration, high cost formanufacturing, inconvenience for use and functional inadequacy.

The patent of invention of filing No. 94101555.6 disclosed a disposablesafety syringe, including a protective casing, which is moveably sleevedon the outside of a syringe barrel to make itself be able to move froman inactivated contracted position to a safety position in the front.Where it is at the inactivated contracted position, a needle protrudesfrom the protective casing, which has a fixation device to automaticallyretain the protective casing at the safety position in the front so thatthe protective casing cannot contract with respect to the syringebarrel. Such an invention can protect the needle, yet it has thefollowing problems:

First, the overall configuration of the invention is complicated;thereby making its dies possess complex structures that shorten theservice life of the dies. As a result, the investment on manufacture andcost goes up.

The second, the invention comprises many parts, which raise thedifficulty of assembly process as well as production cost.

The third, the invention only carries out a protection for the needle.Yet no auto-latching and auto-disable functions regarding to the wholesyringe are implemented. Therefore, some other parts (e.g. plunger) thatmight be taken off to reuse are still latent safety problems topatients.

The fourth, the invention reserves a defined space at the front end ofthe syringe, thereby bringing a considerable inconvenience for someapplications of the syringe, e.g. blood withdrawal.

SUMMARY

The present invention aims to provide a safety syringe of a simplestructure at low cost, which can be used conveniently. The safetysyringe does not only have needle-protective functionality and is alsoauto-disable.

To implement a syringe that meets the aforementioned aims, the presentinvention adopts the following technical schemes. The safety syringecomprises a sliding casing, a needle, a syringe barrel, a piston, aspring and a plunger provided inside the syringe barrel, at the frontend of which a luer tip with a needle luer skirt thereon to engage withthe needle and is provided; the needle is installed on the luer tip atthe front end of the syringe barrel through the needle luer skirt; aconnection head is provided at the front end of the plunger to attach tothe piston; the syringe is characterized in that the sliding casing ismoveably sleeved on the outside of the syringe barrel, two elasticextension plates are provided at the rear end of the sliding casing, oneach of the elastic extension plates a respective connection part isprovided; At least one short groove is formed in the middle of thesliding casing; Two elastic locking plates are provided at the shortgroove; Also, a reduced section is formed at the front end of thesliding casing; In the middle of a guard board that is provided at thefront end of the reduced section, a hole permitting the needle toprotrude is formed; A vertical ringy face is provided at the front endof the syringe barrel; A long groove engaging with the elastic lockingplates is formed on the surface of the syringe barrel; At the frontportion of the long groove, a position limiting plate is provided; Theposition limiting plate can be locked between the two elastic lockingplates; Two connecting portions are formed on the surface of the syringebarrel respectively corresponding to the connection parts on the elasticextension plates so that the connecting portions can respectively fitand connect with the connection parts on the elastic extension plates; Aoff-locking plate is provided to the plunger to correspond to theelastic extension plates of the sliding casing; In the opposite planesof the off-locking plate and the elastic extension plates of the slidingcasing at least one is a slant face; When the off-locking plate and theelastic extension plates of the sliding casing contact with each other,the off-locking plate may make the elastic extension plates of thesliding casing opening towards its two sides under the action of theslant face; The spring is sleeved on the outer casing of the needle luerskirt of the syringe barrel and compressed between the guard board ofthe sliding casing and the vertical ringy face of the syringe barrel.

In the above safety syringe, the rear portion of the syringe barrel isprovided with at least two resistance rings. Furthermore, the syringealso includes a latching casing whose front end is a tapered facecontracted inward and is provided with at least two long grooves. Inaddition, a locking ring is formed at the central portion of the surfaceof the latching casing. The latching casing is installed at the rearportion of the inner hole of the syringe barrel and is sleeved on theplunger. The main body of the plunger is a “+” (across) shaped rib plateincluding a front “+” shaped rib plate, a middle “+” shaped rib plate, astepped resistance plate and a rear “+” shaped rib plate. The outlinesize of the front “+” shaped rib plate is slightly larger than the innerdiameter of the front end of the latching casing, the outline size ofthe middle “+” shaped rib plate is smaller than the diameter of theinner hole at the front end of the latching casing, the number of thestepped resistance plate is at least one, and the outer diameter thereofis slightly larger than the diameter of the inner hole at the front endof the latching casing.

In the aforementioned safety syringe, a front resistance ring of atriangular cross-section and a rear resistance ring of atrapezoid-shaped cross-section are provided at the rear portion of theinner hole of the syringe barrel. The front resistance ring has atriangular cross-section and the inner diameter thereof is slightlysmaller than the inner diameter of the syringe barrel. The angle betweenthe frontal slant face of the front resistance ring and the axis of thesyringe barrel is small, whereas the angle between the rear slant faceof the front resistance ring and the axis of the syringe barrel islarge. The rear resistance ring has a trapezoid-shaped cross-section;the angle between its frontal slant face and the axis of the syringebarrel and the angle between its rear slant face and the axis of thesyringe barrel are both large. The inner diameter of the rear resistancering is smaller than that of the front resistance ring. The front endface of the locking ring of the latching casing is perpendicular to theaxis of the syringe barrel, and the angle between the rear slant facethereof and the axis of the syringe barrel is large. The outer diameterof the locking ring is equal to the inner diameter of the syringebarrel. The width of the locking ring is slightly smaller than thedistance between the front resistance ring and the rear resistance ringin the syringe barrel. The distance between the front end face of thelocking ring of the latching casing and the rear slant face of the frontresistance ring is slightly larger the distance between the front endface of the latching casing and the rear end face of the steppedresistance plate.

In the aforementioned safety syringe, the connection part may be alocking notch formed on the elastic extension plate, the connectingportion is a protruding platform provided on the syringe barrel tocorrespond to the locking notch. The protruding platform can be lockedin the locking notch.

In the aforementioned safety syringe, the connection part of the elasticextension plate may be a “T” shaped plate. The rear end of the syringebarrel is provided with a protruding ring. The connecting portion is agroove formed on the protruding ring to engage with the “T” shaped plateso that the “T” shaped plate can be locked in the groove.

In the aforementioned safety syringe, the connection part of the elasticextension plate may be a bark-shaped plate. The connecting portion ofthe syringe barrel is the rear end face of the syringe barrel and thebark-shaped plate can be is locked on the rear end face of the syringebarrel.

In the aforementioned safety syringe, two long grooves, where individualelastic extension plate is further provided respectively, are formed atthe rear portion of the sliding casing. The connection parts on theelastic extension plates are the locking notches respectively formed onthe elastic extension plates. The connecting portions are protrudingplatforms provided on the syringe barrel to respectively correspond toeach locking notch. The protruding platforms can be locked in thecorresponding locking notches.

In the above safety syringe, the diameter of the inner hole of thepiston is larger than the diameter of the connecting portion of the headof the plunger, the length of the piston is 1˜5 mm larger than thethickness of the connecting portion of the plunger.

In the above safety syringe, a circular anti-pull-off plate is providedon the “+” shaped rib plate of the plunger from where the distance tothe rear stepped plate is equal to the distance from the front end faceof the latching casing to the rear end face of the locking ring. Theouter diameter of the circular anti-pull-off plate is slightly smallerthan the diameter of the inner hole at the rear end of the latchingcasing.

In the above safety syringe, a weak connecting area is provided on therear “+” shaped rib plate. Its two horizontal rib plates are connectedby two small breakable connecting pillars, which are respectivelysymmetric with its centers; while its two vertical rib plates areconnected by a breakable narrow belt.

In the above safety syringe, a transitional slant face or a transitionaltapered platform is between the front “+” shaped rib plate and the rear“+” shaped rib plate of the plunger. The angle between the slant faceand the axis is not less than 30 degrees.

In the above safety syringe, the end portions of the two elastic lockingplates at the short groove of the sliding casing protrude towards theinner hole, the protruding height is slightly larger than the depth ofthe long grooves in the syringe barrel. The height of the protrudingplatform of the syringe barrel is smaller than the depth of the lockingnotch. The width of the protruding platform is smaller than that of thelocking notch.

The present invention has the following advantages over the prior artsby adopting the above designs;

The present invention can be easily used to carry out an injection andto initiate its safety mechanism by a single hand. The sliding casingcan be automatically positioned and locked in two directions, thisdesign guarantees during processing the syringe after it is used, thepinhead is always protected by the sliding casing, thereby avoiding suchan occurrence that the pinhead may hurt the operators;

Also, the present invention has a reliable function of auto-locking;therefore, once the syringe is used, the plunger has been locked in thesyringe barrel and cannot be pulled out any longer, any attempt to usethe syringe again will cause the plunger broken and the syringe damaged,thus ensuring a one-time use.

The piston of the present invention can be assembled optimally. Not onlythe structure of the invention is simplified to make operationconvenient (the invention is fully equal to common syringes with respectto injection operation), the invention is but also designed to meet therequirements to control the accuracy of used dosage for injection, toguarantee the operational safety of blood withdrawal, and to make thevariation of pushing force of injection negligible so that the easinessof injection is not affected essentially. Furthermore, initiating thesafety mechanism (to make sliding casing moved forward) will not bestarted until injection is finished, therefore it does not affect thepatients negatively.

The present invention has a simplified structure considering the medicalfluid in the syringe. The parts of syringe that contact with the medicalfluid are only the syringe barrel and the piston (fully equal to commonsyringes), thereby reliably avoiding the medical fluid to becontaminated and guaranteeing the safety of injection.

The present invention makes a change of standard needle easy so that itsatisfies the different requirements of use.

The structures of the parts of the present invention is relativelyconcise among the like safety syringes, so it is convenient formanufacturing and easy for assembling, thus leading to a high costeffectiveness.

The present invention can make the automatic or semi-automatic assemblyeasily realized, thereby creating a better condition for massproduction.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures, which are incorporated in and constitute apart of the specification, illustrating presently preferred embodimentsof the invention. Together with the above general description and thefollowing detailed description, the figures serve to explain theprinciples of the invention.

FIG. 1 is a schematic view of the configuration of the presentinvention;

FIG. 2 is a top view of the FIG. 1;

FIG. 3 is a schematic view of the configuration of the present inventionwhen the fluid is withdrawn;

FIG. 4 is a schematic view of the configuration of the present inventionafter the injection is finished;

FIG. 5 is a schematic view of the configuration of the present inventionwhen it is pulled broken;

FIG. 6 is a schematic view of the configuration of the present inventionthat carries out the functionality of a needle;

FIG. 7 is a schematic view of the configuration of another embodiment ofthe present invention;

FIG. 8 is a top view of the FIG. 7;

FIG. 9 is a schematic view of the configuration of still anotherembodiment of the present invention;

FIG. 10 is a top view of the FIG. 9;

FIG. 11 is a schematic view of the configuration of still anotherembodiment of the present invention; and

FIG. 12 is a top view of the FIG. 11.

DETAILED DESCRIPTION

FIG. 1 and FIG. 2 show a schematic view of the configuration of anembodiment according to the present invention, namely a safety syringein an unused state after its assembly. The syringe comprises a needle 1,a spring 2, a sliding casing 3, a piston 4, a syringe barrel 5, aplunger 6 and a latching casing 7.

The injection needle 1 may be engaged with a needle luer skirt 51 at thefront end of the syringe barrel 5 by screwing the flange 11 on theneedle base so that the inner hole 12 of the needle base engages with aluer tip 52 of the syringe barrel.

The sliding casing 3 is moveably sleeved on the outside of the syringebarrel 5. The rear portion of the sliding casing 3 is provided with twoelastic extension plates 31, on each of which a connection part isrespectively provided. In this embodiment, the connection part is alocking notch 311 respectively grooved on each of the extension plates31. The middle portion of the sliding casing has two short grooves 32,on each of which an elastic locking plate 321 and an elastic lockingplate 322 are respectively provided. The front end of the sliding casing3 is a reduced section 33, at the front of which a guard board 34 isprovided and a hole 35 permitting the needle to reach out is provided inthe center of the guard board 34.

A vertical ringy face 53 is provided in the front end of the syringebarrel 5, on whose surface two long grooves 54 are provided for engagingwith the elastic locking plates 321 and 322 respectively. A respectiveposition limiting plate 55 is provided at the front end of each longgroove 54. The end portion of each elastic locking plate 321 or 322protrudes toward the inner hole, the protruding length is slightlylarger than the depth of the long groove 54 in the syringe barrel sothat the end portion of the elastic locking plate 321 or 322 canrespectively slide in the long grooves 54. Furthermore, the positionlimiting plate 55 can be locked between the elastic locking plates 321and 322.

The rear portion of the inner side of the syringe barrel 5 is providedwith two resistance rings 56 and 57. The cross section of the frontresistance ring 56 is a triangular and its inner diameter is slightlysmaller than the inner diameter of the syringe barrel 5. The front slantface of the front resistance ring 56 holds a 10-degree angle withrespect to the axis and its rear slant face is perpendicular to theaxis. The cross section of the rear resistance ring 57 is a trapezoidand both its front slant face and its rear slant face has a 45-degreeangle with respect to the axis of the syringe barrel. The inner diameterof the rear resistance ring 57 is smaller than the inner diameter of thefront resistance ring 56. A connecting portion is respectively providedon the outside of the syringe barrel 5 to correspond to the connectionpart of the elastic extension plate 31. In this embodiment, theconnecting portion is provided on a protruding platform 58 on the rearportion of the syringe barrel 5 to correspondingly engage with thelocking notch 311 of the elastic extension 31. The height of theprotruding platform 58 is smaller than the depth of the locking notch311 and the width of the protruding platform 58 is smaller than thewidth of the locking notch 311. Furthermore, the protruding platform 58can be locked in the locking notch 311. In addition, a transitionaltapered plane is provided between the vertical ringy face 52 and thesurface of the syringe barrel 5 with a view to easily assembling.

The latching casing 7 is installed at the rear portion of the inner holeof the syringe barrel 5 and sleeved on the plunger 6. The front portionof the latching casing 7 is a hollowed tapered elastic plate 71contracted inward and has three or four long grooves in it. A lockingring 72 is provided on the surface in the middle part of the latchingcasing 7. The perpendicular axis of the front end face of the lockingring 72 and the rear slant face thereof form a 45-degree angle with theaxis respectively. The outer diameter of the locking ring 72 is equal tothe diameter of the inner hole of the syringe barrel 5. The width of thelocking ring 72 is slightly smaller than the width between the frontresistance ring 56 and the rear resistance ring 57 inside the syringebarrel.

The “+” shaped rib plate of the plunger 6 is formed into severalsections with different structures and sizes, namely, a front “+” shapedrib plate 62, a middle “+” shaped rib plate 63, a stepped resistanceplate 64 and a rear “+” shaped rib plate 65. The front “+” shaped ribplate 62 has an outline size that is slightly larger than the diameterof the inner hole at the front end of the latching casing, while themiddle “+” shaped rib plate 63 has an outline size that is smaller thanthe diameter of the inner hole at the front end of the latching casing.Between the front “+” shaped rib plate 62 and the middle “+” shaped ribplate is a transitional slant face 621 (or a tapered plane), which holdsa 45-degree angle with respect to the axis. Also, between the uniquelyprovided stepped resistance plate 64 and the middle “+” shaped rib plate63 is another transitional slant face 631, which holds a 15-degree anglewith respect to the axis. A circular anti-pull-off plate 66 whose outerdiameter is slightly smaller than the diameter of the inner hole at therear end of the latching casing 7 is provided at a place on the rear “+”shaped rib plate 65 from which the distance to the stepped resistanceplate 64 is equal to the distance from the front end face of thelatching casing 7 to the rear end face of the locking ring 72. A weakconnecting area 67 is provided on the anti-pull-off plate 66 of the rear“+” shaped rib plate 65, between the horizontal rib plates are two smallbreakable connecting pillars the perpendicular rib plates. A taperedoff-locking plate 68 is provided on the rear “+” shaped rib plate 65 tocorrespond to the elastic extension plate 31 of the sliding casing 3. Atleast one opposite plane of the off-locking plate 68 and the elasticextension plate 31 is a slant face. When the off-locking plate 68contacts with the elastic extension plate 31 of the sliding casing, theoff-locking plate 68 affected by the slant face may make the elasticextension plate 31 slightly opening towards its two sides. In thisembodiment, the end face of the elastic extension plate 31 isperpendicular to the axis, while the off-locking plate is a taperedplate whose small end diameter is smaller than the inner diameter of thesliding casing 3 and whose large end diameter is larger than the innerdiameter of the sliding casing 3.

The same result that the off-locking plate 68 pushes the elasticextension plate 31 to open towards its two sides may be also obtained byletting the end face of the elastic extension plate 31 be a slant faceand the off-locking plate 68 be a cylindrical plate. Therefore, each ofthe two designs mentioned above falls into the scope of protection underthe present invention.

The spring 2 is sleeved on an outer casing 50 of the needle luer shirtof the syringe barrel and is compressed between the guard board 34 ofthe sliding casing and the vertical ringy face 53 of the syringe barrel.Since the spring 2 is defined by the inner hole of the reduced section33 of the sliding casing and is held by the surface plane of the outercasing 50 of the needle luer shirt at the front end of the syringebarrel, the spring cannot be distorted laterally and affected regardingthe elasticity.

The diameter of the inner hole of the piston 4 is larger than thediameter of the connection part 611 of the plunger head 61, while thelength of the inner hole of the piston is larger than the thickness (4mm) of the connection part 611 of the plunger.

Furthermore, the distance from the front end face of the locking ring 72of the latching casing 7 to the rear slant face of the front resistancering 56 should slightly larger than the distance from the front end faceof the latching casing 7 to the rear end face of the stepped resistanceplate 64.

FIG. 3 shows the situation when syringe is being used. Afluid-withdrawal (or blood-withdrawal) can be realized by letting theplunger 6 to move back, which in turn brings the piston 4 to move,thereby forming a vacuum inside the front portion of the syringe barrel.When the plunger is pulled to the extent that the transitional slantface of the plunger touches the front end face of the latching casing,the plunger brings the latching casing 7 to move back along the frontslant face of the front resistance ring 56. Since the height of thefront resistance ring 56 is small, the angle of the front slant facethereof is very small, the angle of the transitional slant face 621 ofthe plunger is large, the latching casing 7 can overcome a resistancefrom the front resistance ring 56 and slide back. However, when thelocking ring 72 on the latching casing 7 slips into between the frontresistance ring 56 and the rear resistance ring 57 of the syringebarrel, because the inner diameter of the rear resistance ring 57 issmall and the angle between its front slant face and the axis is large,the increased resistance makes the latching casing 7 not move back anylonger. The front portion of the latching casing 7 has a greatelasticity, therefore, the front elastic plate 71 can distort under theaction of the transitional slant face 621 and move across thetransitional slant face 621 of the plunger until it slides to thesurface of the front “+” shaped rib plate 62 before the plunger so thatthe fluid-withdrawal (or blood-withdrawal) can be continued until theoperational process is finished. It is clear that the syringe utilizes anecessary pull-back action on the plunger to realize the functionalpositioning of the latching casing 7; furthermore, since the rear endface of the front resistance ring 56 is perpendicular to the axis andthe front end face of the locking ring 72 on the latching casing 7 isalso perpendicular to the axis, the latching casing 7 having realizedthe functional positioning can not move back and forth any longer.

FIG. 4 show that the embodiment functions the same as common syringes inan operational process of pushing a medical fluid. The plunger 6 pushesthe piston 4 to move forward inside the syringe barrel so that themedical fluid therein can be injected into a human body through thesyringe barrel 5 and the needle 1; Consequently, the front end face ofthe latching casing is moved back, the stepped resistance plate 64 onthe plunger 6 goes through the inner hole of the elastic plate 71 at thefront end of the latching casing ; Since the frontal elastic plate 71 ofthe latching casing 7 has a good elasticity, the resistance received bythe plunger 6 is relatively low, thereby causing the pushing force ofthe injection insignificantly changed; Put it another way, nouncomfortable feeling is accompanied during the injection; When thefront end face of the piston 4 is reached to the front wall of the innerhole of the syringe barrel, the injection is finished. As a result, theplunger 6 is defined inside the syringe barrel 5 by the latching casing7 and cannot be pulled out again. If the plunger 6 is withdrawn, therear end face of the stepped resistance plate 64 thereon may touch thefront end face of the latching casing 7. Because both the two end facesare perpendicular to the axis, a great resistance can be generated.However, the size of the anti-pull-off plate 66 of the plunger 6 issimilar to that of the inner hole of the latching casing 7, therebyavoiding the locking ring 72 on the latching casing to detach from thefront resistance ring 56 and the rear resistance ring 57 due to itscontracting movement inward. If the pulling force is further increased,the plunger 6 may break at the connecting pillars on the horizontal ribplate in the weak connecting area 67 or at the thin connecting belt anddamage, thereby avoiding a reuse of the syringe (as in FIG. 5).

The FIG. 6 shows that in a normal operation, if the plunger 6 is furtherpushed forward a little after the injection (or the syringe is withdrawnfrom the patient's body), the transitional cylinder 41 of the piston canbe compressed because the thickness of the connection part 61 of theplunger is smaller than the length of the inner hole of the piston 4;Put it another way, the plunger 6 can keep moving forward for about 1 to3 mm; Also, because the off-locking plate 68 on the plunger 6 is closeto or in contact with the end portion of the elastic extension plate 31of the sliding casing after the injection, when the plunger is furthermoved forward, the slant face 681 on the plunger may touch the endportion of the elastic extension plate 31 to push the extension plate 31move outward; As a result, the end face of the locking notch 311 incontact with the end face of the protruding platform 58 of the syringebarrel is also moved outward; When the amount of the movement is largerthan the height of the protruding platform, the sliding casing 3 and thesyringe barrel 5 may slide with respect to each other under the actionof the spring 2; Due to the sliding distance which is larger than thelength of a section of the needle protruding from the front end of thesliding casing 3, the pinhead 11 of the needle 1 is covered inside thesliding casing 3, thereby avoiding the pinhead to hurt people andrealizing the safety protection function for the syringe needle.Obviously, at this moment, the front elastic locking plate 321 of thesliding casing has crossed over the position limiting plate 55 on thesyringe barrel (because the distance between the two elastic lockingplates is larger than the thickness of the position limiting plate 55)and is on the left of the front end face of the position limiting plate55 so as to stop the sliding casing to move backward, thereby definingthe sliding casing 3 at a position shown in the FIG. 6 and realizing areliable safety functionality.

In addition, as shown in the figures, the wing plate 36 is installed onthe sliding casing 3; that means an index finger and a middle finger ofan operator are respectively placed at each side of the wing plate 36.Therefore, once the sliding casing 3 and the syringe barrel 5 give arelative movement, it is the truth that the syringe barrel 5 is movedbackward and is pulled into the sliding casing 3 together with theneedle 1. Such a configuration has advantages that if the safetymechanism is initiated so that the needle can be automatically pulledout from the human body, while the sliding casing does not move forwardto touch human body and does not bring patients painful oruncomfortable. It is obvious that installing the wing plate 36 on thesyringe barrel 5 is another feasible structure.

FIG. 7 and FIG. 8 show a schematic view of the configuration of anotherembodiment of the present invention. Its main changes compared to theembodiment provided from FIG. 1 to FIG. 6 include that the connectionpart of the elastic extension plate of the sliding casing 3 is a “T”shaped plate 31′; a protruding ring 58′ is provided at the rear end ofthe syringe barrel 5; the connecting portion on the syringe barrel is agroove 581′ formed on the protruding ring 58′ to engage with the “T”shaped plate 31′; and the “T” shaped plate 31′ can be locked in thegroove 581′. After the syringe is used, the off-locking plate 68similarly pushes the end face of the elastic extension plate so that theelastic extension plate is slightly opened outward, thereby making a “T”shaped head 312 detach with from the groove 581′; As a result, thesliding casing 3 and the syringe barrel 5 have a sliding movement withrespect to each other under the action of the spring 2, causing theneedle to be protected.

Further, FIG. 9 and FIG. 10 show a schematic view of the configurationof still another embodiment of the present invention. Its main changescompared to the embodiment provided from FIG. 1 to FIG. 6 include theconnection part of the elastic extension plate of the sliding casing 3is a bark-shaped plate 31″, which may be bark-fixed on the rear end faceof the syringe barrel 5. After the syringe is used, the off-lockingplate 68 similarly pushes the end face of the elastic extension plate sothat the elastic extension plate is slightly opened outward, therebymaking the bark 313 of the elastic extension plate unhooked from therear end face of the syringe barrel 5; As a result, the sliding casing 3and the syringe barrel 5 have a sliding movement with respect to eachother under the action of the spring 2, causing the needle to beprotected.

Furthermore, FIG. 11 and FIG. 12 show a schematic view of theconfiguration of still another embodiment of the present invention. Itsmain changes compared to the embodiment provided from FIG. 1 to FIG. 6include two grooves 37 formed on the rear portion of the sliding casing3; a respective elastic extension plate 31 is provided at two grooves37; The respective connection part on each elastic extension plate 31 isthe a locking groove 311 formed on the elastic extension plate; aconnecting portion is a protruding platform 58 provided on the syringebarrel 5 to engage with the locking groove 311; and the protrudingplatform 58 can be locked in the locking groove 311.

INDUSTRIAL APPLICABILITY

The present invention can be easily used to carry out an injection andto initiate its safety mechanism by a single hand. The sliding casingcan be automatically positioned and locked in two directions. Thisdesign guarantees during processing the syringe after it is used, thepinhead is always protected by the sliding casing, thereby avoiding suchan occurrence that the pinhead may hurt the operators; Also, the presentinvention has a reliable function of auto-locking, therefore, once thesyringe is used, the plunger has been locked in the syringe barrel andcannot be pulled out any longer; any attempt to use the syringe againwill cause the plunger broken and the syringe damaged, thus ensuring aone-time use. Among the like safety syringes, the invention has aconcise configuration for parts, which is convenient for manufacturingand is easy for assembling, therefore the invention has significantfeatures such as high performance and low cost. Furthermore, theconfiguration of the present invention can easily realize automatic orsemi-automatic assembly, which creates a good condition for massproduction.

1. A safety syringe including a sliding casing, a needle, a syringebarrel, a piston, a spring, and a plunger inside the syringe barrel; aluer tip with a needle luer skirt thereon provided at the front end ofthe syringe barrel to mate with the needle that is installed on the luertip at the front end of the syringe barrel through the needle luerskirt, with the front end of the plunger having a connection part toengage with the piston, is characterized in that: the sliding casing ismoveably sleeved on the outside of the syringe barrel, with two elasticextension plates on each of which a connection part is respectivelybeing provided at the rear portion of the sliding casing; the front endof the sliding casing is a reduced section whose front end has a guardboard whose center is provided with a hole permitting the needle toreach out; a vertical ringy face is provided at the front end of thesyringe barrel whose surface has a long groove to engage with elasticlocking plates, the front portion of the long groove is provided with aposition limiting plate that can be locked between the two elasticlocking plates; the outside surface of the syringe barrel is providedwith two connecting portions to respectively correspond to theconnection part of each elastic extension plate, the connecting portionscan engage with the connection parts on the elastic extension platesrespectively; the plunger is provided with a sliding casing off-lockingplate corresponding to the elastic extension plate of the slidingcasing, at least one opposite faces of the sliding casing off-lockingplate and the elastic extension plate of the sliding casing is a slantface; when the sliding casing off-locking plate and the elasticextension plate of the sliding casing is in contact with each other, thesliding casing off-locking plate may make the said elastic extensionplate of the sliding casing opening toward its two sides under theaction of the slant face; the spring is sleeved on the casing of theneedle luer shirt of the syringe barrel and is compressed between theguard board of the sliding casing and the vertical ringy face of thesyringe barrel.
 2. The safety syringe according to claim 1, wherein thesyringe barrel is provided with at least two resistance rings at itsrear portion; the syringe further includes a latching casing whose frontportion is a tapered plane contracted inward with at least two longgrooves thereon and whose surface is provided with a locking ring in thecentral section; the latching casing is installed at the rear portion ofan inner hole of the syringe barrel and is sleeved on the plunger; themain body of the plunger is a “+” shaped rib plate including a front “+”shaped rib plate, a middle “+” shaped rib plate, a stepped resistanceplate and a rear “+” shaped rib plate; the outline size of the front “+”shaped rib plate is slightly larger than the diameter of the inner holeat the front end of the latching casing, the outline size of the middle“+” shaped rib plate is smaller than the diameter of the inner hole atthe front end of the latching casing, the number of the steppedresistance plate whose outer diameter is slightly larger than thediameter of the inner hole at the front end of the latching casing is atleast one.
 3. The safety syringe according to claim 2, wherein the rearportion of the inner hole of the syringe barrel has a front resistancering with a triangular cross section and a rear resistance ring with atrapezoid-shaped cross section; the cross section of the frontresistance ring is triangular and its inner diameter is slightly smallerthan the inner diameter of the syringe barrel, the angle between thefront slant face of the front resistance ring and the axis is small, theangle between the rear slant face and the axis is large; the crosssection of the rear resistance ring is trapezoid-shaped, the front slantface and the rear slant face of the rear resistance ring respectivelyhold a large angle with respect to the axis of the syringe barrel, theinner diameter of the rear resistance ring is smaller than the innerdiameter of the front resistance ring; the front end face of the lockingring of the latching casing is perpendicular to the axis, the anglebetween the rear slant face and the axis is large, the outer diameter ofthe locking ring equals to the diameter of the inner hole of the syringebarrel, the width of the locking ring is slightly smaller than the widthbetween the front resistance ring and the rear resistance ring insidethe syringe barrel; the distance from the front end face of the lockingring of the latching casing to the rear slant face of the frontresistance ring is slightly larger than the distance from the front endface of the latching casing to the rear end face of the steppedresistance plate of the plunger.
 4. The safety syringe according toclaims 3, wherein the connection part is the locking notch formed on theelastic extension plate, the connecting portion is a protruding platformprovided on the syringe barrel to correspond to the locking notch, theprotruding platform can be locked in the locking notch.
 5. The safetysyringe according to claim 4, wherein the connection part of the elasticextension plate is a “T” shaped plate, a protruding ring is provided atthe rear end of the syringe barrel, the connecting portion is a grooveformed on the protruding ring to engage with the “T” shaped plate, the“T” shaped plate can be locked in the groove.
 6. The safety syringeaccording to claim 4, wherein the connection part of the elasticextension plate is a bark-shaped plate, the connecting portion of thesyringe barrel is the rear end face of the syringe barrel on which thebark-shaped plate may be locked.
 7. The safety syringe according toclaim 4, wherein the rear portion of the sliding casing is provided withtwo grooves, the two grooves are respectively provided with the elasticextension plate, the connection part on the elastic extension plate isthe locking notch provided on the elastic extension plate, theconnecting portion is a protruding platform provided on the syringebarrel to correspond to the locking notch in which the protrudingplatform can be locked.
 8. The safety syringe according to claim 5,wherein the diameter of the inner hole of the piston is larger than thediameter of the connection part of the head of the plunger and thelength of the inner hole is 1 to 5 mm larger than the thickness of thehead of the plunger.
 9. The safety syringe according to claim 6, whereinthe diameter of the inner hole of the piston is larger than the diameterof the connection part of the head of the plunger and the length of theinner hole is 1 to 5 mm larger than the thickness of the head of theplunger.
 10. The safety syringe according to claim 7, wherein thediameter of the inner hole of the piston is larger than the diameter ofthe connection part of the head of the plunger and the length of theinner hole is 1 to 5 mm larger than the thickness of the head of theplunger.
 11. The safety syringe according to claim 5, wherein the rear“+” shaped rib plate of the plunger is provided with a circularanti-pull-off plate from which the distance to the rear stepped plate isequal to the distance from the front end face of the latching lockcasing to the rear end face of the locking ring, and the outer diameterof the circular anti-pull-off plate is slightly smaller than thediameter of the inner hole at the rear end of the latching casing. 12.The safety syringe according to claim 6, wherein the rear “+” shaped ribplate of the plunger is provided with a circular anti-pull-off platefrom which the distance to the rear stepped plate is equal to thedistance from the front end face of the latching lock casing to the rearend face of the locking ring, and the outer diameter of the circularanti-pull-off plate is slightly smaller than the diameter of the innerhole at the rear end of the latching casing.
 13. The safety syringeaccording to claim 7, wherein the rear “+” shaped rib plate of theplunger is provided with a circular anti-pull-off plate from which thedistance to the rear stepped plate is equal to the distance from thefront end face of the latching lock casing to the rear end face of thelocking ring, and the outer diameter of the circular anti-pull-off plateis slightly smaller than the diameter of the inner hole at the rear endof the latching casing.
 14. The safety syringe according to claim 10,wherein the rear “+” shaped rib plate of the plunger is provided with acircular anti-pull-off plate from which the distance to the rear steppedplate is equal to the distance from the front end face of the latchinglock casing to the rear end face of the locking ring, and the outerdiameter of the circular anti-pull-off plate is slightly smaller thanthe diameter of the inner hole at the rear end of the latching casing.15. The safety syringe according to claim 5, wherein the respective endportion of two elastic locking plates at the short groove of the slidingcasing protrudes toward the inner hole and the protruding height isslightly larger than the depth of the long groove in the syringe barrel;the height of the protruding platform is not smaller than the depth ofthe locking notch and the width of the protruding platform is smallerthan the width of the locking notch.
 16. The safety syringe according toclaim 6, wherein the respective end portion of two elastic lockingplates at the short groove of the sliding casing protrudes toward theinner hole and the protruding height is slightly larger than the depthof the long groove in the syringe barrel; the height of the protrudingplatform is not smaller than the depth of the locking notch and thewidth of the protruding platform is smaller than the width of thelocking notch.
 17. The safety syringe according to claim 7, wherein therespective end portion of two elastic locking plates at the short grooveof the sliding casing protrudes toward the inner hole and the protrudingheight is slightly larger than the depth of the long groove in thesyringe barrel; the height of the protruding platform is not smallerthan the depth of the locking notch and the width of the protrudingplatform is smaller than the width of the locking notch.
 18. The safetysyringe according to claim 14, wherein the respective end portion of twoelastic locking plates at the short groove of the sliding casingprotrudes toward the inner hole and the protruding height is slightlylarger than the depth of the long groove in the syringe barrel; theheight of the protruding platform is not smaller than the depth of thelocking notch and the width of the protruding platform is smaller thanthe width of the locking notch. 19-36. (canceled)